Add the saffron to the chicken stock and bring to a simmer in a large saucepot.

Heat the olive oil in a large Paella pan over medium-high heat and season the chicken liberally with salt and pepper. Carefully brown the chicken thighs in the pan until golden brown on both sides. Add the onion and red pepper and gently sauté until translucent. Add chorizo and then the grated tomato and simmer for 10 minutes until slightly reduced.

Add the rice and carefully distribute throughout the pan, then add the very hot stock until the rice is covered. Season liberally with salt and reduce to a rolling simmer for 15 minutes or until most of the stock is absorbed. Add more stock as needed until the rice is just cooked through- about 30 minutes.

When the rice has just a little "tooth" still, add the shell fish, burying the mussels and clams into the rice to steam them. When the mussels and clams have all opened and the rice is cooked through, turn the heat up high for 2 to 3 minutes to get the "socarrat" or crust. Remove from heat and let cook for 5 minutes before serving.